Concurrent method for resonant frequency detection in corona ignition systems

ABSTRACT

A system and method for detecting resonant frequency of a corona igniter concurrent with operation of the corona igniter is provided. The method includes providing a plurality of pulses of energy to the corona igniter, each having a pulse duration and spaced from one another by a deadtime duration during which no energy is provided to the corona igniter. Each pulse duration is ceased before current flowing in the corona igniter crosses zero, and each zero crossing of the current occurs during one of the deadtime durations. The next pulse of energy is provided to the corona igniter in response to the zero crossing of the current. A resonant frequency value is then obtained based on a sum of the pulse and deadtime durations of two consecutive cycles, or the time between zero crossings. The resonant frequency values become more accurate over time, and the drive frequency is adjusted accordingly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. continuation patent application claims the benefit of U.S.utility patent application Ser. No. 14/568,219, which claims the benefitof U.S. provisional patent application No. 61/915,088, filed Dec. 12,2013; U.S. provisional patent application No. 61/931,131, filed Jan. 24,2014; U.S. provisional patent application No. 61/950,991, filed Mar. 11,2014; U.S. provisional patent application No. 62/072,530, filed Oct. 30,2014; and U.S. provisional patent application No. 62/090,096, filed Dec.10, 2014, the entire contents of each being incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates generally to a corona discharge ignition system,and more particularly to methods for controlling energy supplied to thecorona igniter system.

2. Related Art

Corona discharge ignition systems provide an alternating voltage andcurrent, reversing high and low potential electrodes in rapid successionwhich enhances the formation of corona discharge and minimizes theopportunity for arc formation. The system includes a corona igniter witha central electrode charged to a high radio frequency voltage potentialand creating a strong radio frequency electric field in a combustionchamber. The electric field causes a portion of a mixture of fuel andair in the combustion chamber to ionize and begin dielectric breakdown,facilitating combustion of the fuel-air mixture, which is referred to asan ignition event. The electric field is preferably controlled so thatthe fuel-air mixture maintains dielectric properties and coronadischarge occurs, also referred to as a non-thermal plasma. The ionizedportion of the fuel-air mixture forms a flame front which then becomesself-sustaining and combusts the remaining portion of the fuel-airmixture. Preferably, the electric field is controlled so that thefuel-air mixture does not lose all dielectric properties, which wouldcreate thermal plasma and an electric arc between the electrode andgrounded cylinder walls, piston, metal shell, or other portion of theigniter. An example of a corona discharge ignition system is disclosedin U.S. Pat. No. 6,883,507 to Freen.

In addition, the corona discharge ignition system is preferablycontrolled so that energy is provided to the corona igniter at a drivefrequency equal or close to the resonant frequency of the coronaigniter. This provides a voltage amplification leading to robust coronadischarge in the combustion chamber. Accurately detecting the resonantfrequency of the corona igniter is necessary in order to achieve thishigh level of control. However, accurate detection of the resonantfrequency it is difficult to achieve, especially at a wide range offrequencies. Changes in the resonant frequency during operation, forexample due to arcing events, also make it difficult to accuratelydetect the resonant frequency.

SUMMARY OF THE INVENTION

One aspect of the invention provides an improved method for detectingthe resonant frequency of a corona igniter concurrent with operation ofthe corona igniter in a corona ignition system. The method includesproviding a first pulse of energy to a corona igniter at a positivevoltage for a first pulse duration causing causes current to flow in thecorona igniter; and ceasing the first pulse duration before the currentflowing in the corona igniter crosses through zero. A first deadtimeduration occurs immediately upon ceasing the first pulse duration, andno energy is provided to the corona igniter during the first deadtimeduration. The method further includes detecting when the current flowingin the corona igniter crosses through zero during the first deadtimeduration; and providing a second pulse of energy to the corona igniterat a negative voltage for a second pulse duration in response to thezero crossing of the current to cease the first deadtime duration. Themethod then includes ceasing the second pulse duration before thecurrent crosses through zero. A second deadtime duration occursimmediately upon ceasing the second pulse duration, and no energy isprovided to the corona igniter during the second deadtime duration. Themethod further includes detecting when the current flowing in the coronaigniter crosses through zero during the second deadtime duration; andproviding a third pulse of energy to the corona igniter at a positivevoltage in response to the zero crossing of the current to cease thesecond deadtime duration. The method then includes obtaining a firstresonant frequency value based on a sum of the first pulse duration, thefirst deadtime duration, the second pulse duration, and the seconddeadtime duration.

Another aspect of the invention provides a method for detecting theresonant frequency of a corona igniter in a corona ignition system,comprising the steps of: providing a first pulse of energy to a coronaigniter at a positive voltage causing causes current to flow in thecorona igniter; ceasing the first pulse before the current flowing inthe corona igniter crosses through zero and providing no energy to thecorona igniter for a first deadtime duration immediately upon ceasingthe first pulse of energy; and obtaining a first zero crossing duration,wherein the first zero crossing duration begins at the start of thefirst pulse of energy and ends at the first zero crossing. The methodfurther includes obtaining a first resonant frequency value by doublingthe first zero crossing duration.

Another aspect of the invention provides a method for detecting theresonant frequency of a corona igniter in a corona ignition system,comprising the steps of: providing a first pulse of energy to a coronaigniter at a positive voltage causing causes current to flow in thecorona igniter; ceasing the first pulse before the current flowing inthe corona igniter crosses through zero and providing no energy to thecorona igniter for a first deadtime duration immediately upon ceasingthe first pulse of energy; and obtaining a first zero crossing duration,wherein the first zero crossing duration begins at the start of thefirst pulse of energy and ends when the current flowing in the coronaigniter crosses through zero during the first deadtime duration. Themethod next includes providing a second pulse of energy to the coronaigniter at a negative voltage in response to the first zero crossing ofthe current to cease the first deadtime duration; ceasing the secondpulse of energy before the current crosses through zero and providing noenergy to the corona igniter for a second deadtime duration immediatelyupon ceasing the second pulse of energy; and obtaining a second zerocrossing duration, wherein the second zero crossing duration begins atthe first zero crossing and ends when the current flowing in the coronaigniter crosses through zero during the second deadtime duration. Themethod then includes obtaining a first resonant frequency value based ona sum of the first zero crossing duration and the second zero crossingduration.

Another aspect of the invention provides a system for detecting theresonant frequency of a corona igniter. The system includes a firstswitch providing a first pulse of energy from an energy supply to acorona igniter at a positive voltage for a first pulse duration causingcurrent to flow in the corona igniter. The first switch ceases the firstpulse duration before the current in the corona igniter crosses throughzero. No energy is provided to the corona igniter for a first deadtimeduration which occurs immediately upon ceasing the first pulse duration.A frequency detector detects when the current flowing in the coronaigniter crosses through zero during the first deadtime duration andinitiates a drive signal to provide a second pulse of energy to thecorona igniter in response to the zero crossing of the current. A secondswitch receives the drive signal and provides the second pulse of energyfrom the energy supply to the corona igniter at a negative voltage for asecond pulse duration to cease the first deadtime duration. The secondswitch ceases the second pulse duration before the current flowing inthe corona igniter crosses through zero. No energy is provided to thecorona igniter for a second deadtime duration which occurs immediatelyupon ceasing the second pulse duration. The frequency detector detectswhen the current flowing in the corona igniter crosses through zeroduring the second deadtime duration and initiates a drive signal toprovide a third pulse of energy to the corona igniter in response to thezero crossing of the current. The first switch receives the drive signaland provides the third pulse of energy from the energy supply to thecorona igniter at a positive voltage to cease the second deadtimeduration. The frequency detector then obtains a first resonant frequencyvalue based on a sum of the first pulse duration, the first deadtimeduration, the second pulse duration, and the second deadtime duration.

Yet another aspect of the invention provides a system for detecting theresonant frequency of a corona igniter in a corona ignition system,comprising a first switch and a frequency detector. The first switchprovides a first pulse of energy from an energy supply to a coronaigniter at a positive voltage causing current to flow in the coronaigniter The first switch then ceasing the first pulse of energy beforethe current in the corona igniter crosses through zero and provides noenergy to the corona igniter for a first deadtime duration immediatelyupon ceasing the first pulse of energy. The frequency detector thenobtains a resonant frequency value by doubling a first zero crossingduration, wherein the first zero crossing duration begins at the startof the first pulse of energy and ends at the first zero crossing.

Another aspect of the invention provides a system for detecting theresonant frequency of a corona igniter in a corona ignition system,comprising a first switch, a second switch, and a frequency detector.The first switch provides a first pulse of energy from an energy supplyto a corona igniter at a positive voltage causing current to flow in thecorona igniter. The first switch ceases the first pulse duration beforethe current in the corona igniter crosses through zero and provides noenergy to the corona igniter for a first deadtime duration immediatelyupon ceasing the first pulse of energy. The frequency detector detectswhen the current flowing in the corona igniter crosses through zeroduring the first deadtime duration and initiates a drive signal toprovide a second pulse of energy to the corona igniter in response tothe first zero crossing of the current. The frequency detector obtains afirst zero crossing duration, wherein the first zero crossing durationbegins at the start of the first pulse of energy and ends at the firstzero crossing. The second switch receives the drive signal and providesthe second pulse of energy from the energy supply to the corona igniterat a negative voltage to cease the first deadtime duration. The secondswitch ceases the second pulse duration before the current flowing inthe corona igniter crosses through zero and provides no energy to thecorona igniter for a second deadtime duration immediately upon ceasingthe second pulse of energy. The frequency detector detects when thecurrent flowing in the corona igniter crosses through zero during thesecond deadtime duration. The frequency detector obtains a second zerocrossing duration, wherein the second zero crossing duration begins atthe first zero crossing and ends at the second zero crossing. Thefrequency detector obtains a first resonant frequency value based on asum of the first zero crossing duration and the second zero crossingduration.

The system and method provide numerous advantages. First, the resonantfrequency values obtained become more accurate over time, and are equalto, or very close to, the actual resonant frequency of the coronaigniter. In addition, the resonant frequency values are obtained whileenergy is being supplied to the corona igniter, and typically while thecorona igniter provides corona discharge. Thus, additional power phaseor measurement periods are not required. Furthermore, the drivefrequency of the energy provided to the corona igniter can beimmediately adjusted concurrent with operation of the corona igniter, orprior to a future corona event, to match the detected resonant frequencyvalue, for example in response to changes caused by arcing events orother conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a block diagram of a corona discharge ignition systemaccording to a first exemplary embodiment of the invention;

FIG. 2 is a block diagram of a corona discharge ignition systemaccording to a second exemplary embodiment of the invention;

FIG. 3 is a block diagram of a corona discharge ignition systemaccording to a third exemplary embodiment of the invention;

FIG. 4 is a graph illustrating current flowing in the corona igniter andvoltage provided to the corona igniter at the beginning of a coronaevent; and

FIG. 5 shows the current flowing in the corona igniter and the voltageprovided to the corona igniter after 20 cycles in the corona event ofFIG. 4.

DETAILED DESCRIPTION

The present invention provides an improved system 20 and method fordetecting the resonant frequency of a corona igniter 22 concurrent withoperation of the corona igniter 22. The resonant frequency valuesobtained using the method are equal to, or very close to, the actualresonant frequency of the corona igniter 22. The drive frequency of theenergy provided to the corona igniter 22 can be adjusted to match thedetected resonant frequency value while the energy is being supplied tothe corona igniter 22 and while the corona igniter 22 provides coronadischarge 26. In addition, immediate adjustments to the drive frequencycan be made during operation of the corona igniter 22 based on thedetected resonant frequency value, for example in response to changescaused by arcing events or other conditions.

Exemplary embodiments of the system 20 capable of implementing theimproved resonant frequency detection are shown in FIGS. 1-3. Thesesystems 20 are also described in related U.S. patent application Ser.Nos. 14/568,219, 14/568,330, and 14/568,438, which are incorporatedherein by reference. In each embodiment, the system 20 includes thecorona igniter 22 coupled to an induction coil L, which are togetherreferred to as the load operating at a resonant frequency. This resonantfrequency is referred to herein as “the resonant frequency of the coronaigniter 22.” The corona igniter 22 receives energy at a drive frequencyand voltage level causing current to flow in the corona igniter 22. Thiscurrent and voltage can be measured at an output 24 of the coronaigniter 22. During operation in an internal combustion engine, thecorona igniter 22 preferably forms a high radio frequency electric fieldat a firing end, referred to as corona discharge 26, to ignite a mixtureof fuel and air in a combustion chamber of the engine.

The system 20 also includes the controller 28 and a pair of switches30A, 30B that control the drive frequency provided to the corona igniter22, and the capacitance/inductance circuit of the system 20, so that thedrive frequency is maintained at or close to the resonant frequency ofthe corona igniter 22. Operating the system 20 such that the drivefrequency is equal to the resonant frequency provides voltageamplification leading to robust corona discharge 26 in the combustionchamber.

The controller 28 of the exemplary embodiments activates one of theswitches 30A or 30B at predetermined times to achieve the desired drivefrequency. When one of the switches 30A or 30B is active, energy canflow from the power supply V3 through the active switch 30A or 30B tothe corona igniter 22. When the switches 30A, 30B are not active, energycannot flow through to the corona igniter 22. Switch 30A is referred toas a first switch, and switch 30B is referred to as a second switch, butthe switch 30B could alternatively be referred to as the first switch,and the switch 30A could be referred to as the second switch. In eachcase, only one of the switches 30A or 30B is active and providing energyto the corona igniter 22 at any given time during operation of thecorona ignition system 20. Thus, the controller 28 deactivates the firstswitch 30A before activating the second switch 30B, and vice versa, sothat the two switches 30A, 30B are not active at the same time.Preferably, activation of the switches 30A, 30B is synchronized with theresonant frequency of the corona igniter 22. For example, in oneembodiment, the first switch 30A is active and thus provides energy tothe corona igniter 22 whenever the current at the output 24 is positive,and the second switch 30B is active and thus provides energy to thecorona igniter 22 whenever the current at the output 24 is negative. Thesystem 20 also includes a frequency detector for detecting the resonantfrequency of the corona igniter 22. The frequency detector is typicallyprovided by a combination of components working together, for examplethe controller 28 working in combination with a current sensor 36, orother components of the system 20.

The method of detecting the resonant frequency is conducted concurrentwith operation of the corona igniter 22 in an internal combustionengine. This this case, the method is conducted while energy is providedto the corona igniter 22 and typically while the corona igniter 22provides corona discharge 26. However, the method can also be conductedat a reduced duty cycle, wherein the energy provided to the coronaigniter 22 is at lower level so that the corona discharge 26 is notcreated. The method could also being at the reduced duty cycle, and theduty cycle can be increased over time.

FIGS. 4 and 5 provide an example of the voltage provided to the coronaigniter 22 and the current flowing in the corona igniter 22 whileimplementing the method of the present invention. FIG. 4 shows thecurrent and voltage at the beginning of a corona event, and FIG. 5 showsthe current and voltage after 20 cycles of the same corona event. The“corona event” is a period of time during energy is provided to thecorona igniter 22 and the corona igniter 22 provides a corona discharge26. These current and voltage levels are used to detect the resonantfrequency of the corona igniter 22, as will be discussed further below.

In general, the method includes employing the first switch 30A toprovide a first pulse of energy from an energy supply, for example V3,to the corona igniter 22. The first pulse of energy is provided at apositive voltage for a first pulse duration 101 causing a positivecurrent to flow in the corona igniter 22. The first switch 30A thenceases the first pulse duration 101 before the current in the coronaigniter 22 crosses through zero, as shown in FIG. 4. The controller 28typically sets the length of the first pulse duration 101 based on anydelays of components of the system 20, so that the first pulse duration101 ends before the current flowing in the corona igniter 22 crossesthrough zero.

A first deadtime duration 201 then occurs immediately upon ceasing thefirst pulse duration 101. No energy is provided from the energy supplyV3, or from any other type of energy source, to the corona igniter 22during the first deadtime duration 201, and the voltage level is at zeroduring the first deadtime duration 201, as shown in FIG. 4. Since theenergy is powered off during the first deadtime duration 201, there areno problems associated with noise in the corona circuit due toswitching.

During the first deadtime duration 201, the frequency detector, such asa combination of the controller 28 and current sensor 36, detects whenthe current flowing in the corona igniter 22 crosses through zero. Thecurrent crosses zero only once during the first deadtime duration 201.In one embodiment, the current sensor 36 obtains the current flowing inthe corona igniter 22 from the output 24 and determines the zerocrossings of the current. This zero crossing measurement is typicallyconveyed from the current sensor 36 to the controller 28 in an outputsignal 54.

The controller 28 receives the output signal 54, and in response to thezero crossing of the current, the controller 28 initiates a drive signal50 to provide a second pulse of energy to the corona igniter 22. Thesecond switch 30B receives the drive signal 50 and provides the secondpulse of energy from the energy supply V3 to the corona igniter 22 at anegative voltage for a second pulse duration 102 to cease the firstdeadtime duration 201. The second switch 30B ceases the second pulseduration 102 before the negative current flowing in the corona igniter22 crosses through zero, as shown in FIG. 4. The controller 28 can alsoset the length of the second pulse duration 102 based on any delays ofcomponents of the system 20, so that the second pulse duration 102 endsbefore the current flowing in the corona igniter 22 crosses throughzero.

A second deadtime duration 202 then occurs immediately upon ceasing thesecond pulse duration 102. No energy is provided from the energy supplyV3, or from any other energy source, to the corona igniter 22 during thesecond deadtime duration 202, and the voltage level during the seconddeadtime duration 202 is at zero, as shown in FIG. 4. The second pulseduration 102 is greater than the first pulse duration 101, and thesecond deadtime duration 202 is less than the first deadtime duration201.

During the second deadtime duration 202, the frequency detector againdetects when the current flowing in the corona igniter 22 crossesthrough zero, in the same manner as during the first deadtime duration201. The current crosses zero only once during the second deadtimeduration 202. In response to the zero crossing of the current, thefrequency detector, typically the controller 28, initiates another drivesignal 50 to provide a third pulse of energy to the corona igniter 22.The first switch 30A receives the drive signal 50 and provides the thirdpulse of energy from the energy supply V3 to the corona igniter 22 at apositive voltage to cease the second deadtime duration 202.

After the second deadtime duration 202, the frequency detector obtains afirst resonant frequency value based on a sum of the first pulseduration 101, the first deadtime duration 201, the second pulse duration102, and the second deadtime duration 202. Typically, the controller 28receives information about the current and voltage from other componentsof the system, and then uses that information to determine the pulsedurations 101, 102 and deadtime durations 201, 202. The controller 28then uses the sum of those durations 101, 102, 201, 202 to determine thefirst resonant frequency value. Various different methods can be used todetermine the first resonant frequency value based on the sum, such asalgorithms performed by software of the controller 28. For example, thestep of obtaining the first resonant frequency value can includedividing the sum in half to determine the duration of one half cycle ofthe resonant frequency. As indicated above, the gathering of informationand evaluation conducted by the controller 28 to obtain the firstresonant frequency value can be conducted during the corona event, whileproviding the energy to the corona igniter 22.

In another embodiment, the frequency detector, such as the currentsensor 36 and the controller 28, determines the first resonant frequencyvalue by obtaining the time between adjacent zero crossings, which caninclude the time between the start of the first pulse of energy and thefirst zero crossing, or the time between two consecutive zero crossings.For example, the controller 28 can obtain the first resonant frequencyvalue by doubling a first zero crossing duration X1. As shown in FIG. 4,the first zero crossing duration X1 begins at the start of a pulse ofenergy and ends at a first zero crossing. The first zero crossing couldbe at startup, as shown in FIG. 4, but could alternatively be the timebetween two later zero crossings.

The controller 28 could alternatively obtain the first resonantfrequency value based on the time between three consecutive zerocrossings, which could be the first three consecutive zero crossings, asshown in FIG. 4, or three later zero crossings. In this embodiment, thecontroller 28 obtains the first zero crossing duration X1 and a secondzero crossing duration X2, wherein the second zero crossing duration X2begins at the first zero crossing and ends at the second zero crossing.The controller 28 obtains a first resonant frequency value based on asum of the first zero crossing duration X1 and the second zero crossingduration X2.

After the first resonant frequency value is obtained, the controller 28can adjust the drive frequency of the energy provided to the coronaigniter 22 to equal the obtained first resonant frequency value,concurrently with operation of the corona igniter 22. The controller 28typically instructs the switches 30A, 30B to provide the energy from theenergy supply V3 to the corona igniter 22 at the first resonantfrequency value while the corona igniter 22 continues to provide thecorona discharge 26. Determining the first resonant frequency value andadjusting the drive frequency to match the obtained first resonantfrequency value can all occur in the same corona event.

The above steps are typically repeated over several cycles or timeperiods, as shown in FIGS. 4 and 5, to obtain additional resonantfrequency values, wherein each consecutive resonant frequency valueobtained is closer to the actual resonant frequency of the coronaigniter 22 than the previous value obtained. Typically, at the start ofeach corona event, as shown in FIG. 4, a reduced duty cycle is used andthe pulse durations are selected to allow a predefined range offrequencies to be accurately detected. The pulse durations are increasedthroughout the process of detecting the resonant frequency values whilethe deadtime durations decrease, as shown in FIGS. 4 and 5, until amaximum pulse duration is achieved. The actual resonant frequency valueof the corona igniter 22 is fully identified when the maximum pulseduration is achieved.

For example, the method can include using the first switch 30A toprovide the third pulse of energy from the energy supply V3 to thecorona igniter 22 for a third pulse duration 103, which is longer thanthe second pulse duration 102; and ceasing the third pulse duration 103before the positive current flowing in the corona igniter 22 crossesthrough zero. No energy is provided to the corona igniter 22 for a thirddeadtime duration 203 immediately upon ceasing the third pulse duration103. The third deadtime duration 203 is shorter than the second deadtimeduration 202.

The frequency detector then detects when the current flowing in thecorona igniter 22 crosses through zero during the third deadtimeduration 203. The second switch 30B provides a fourth pulse of energy tothe corona igniter 22 at a negative voltage for a fourth pulse duration104 in response to the zero crossing of the current to cease the thirddeadtime duration 203. The fourth pulse duration 104 is ceased beforethe current flowing in the corona igniter 22 crosses through zero. Noenergy is provided to the corona igniter 22 for a fourth deadtimeduration 204 immediately upon ceasing the fourth pulse duration 104.

Next, the frequency detector detects when the current flowing in thecorona igniter 22 crosses through zero during the fourth deadtimeduration 204, and provides a fifth pulse of energy to the corona igniter22 at a positive voltage and for a fifth pulse duration 105 in responseto the zero crossing of the current to cease the fourth deadtimeduration 204. The fourth pulse duration 104 is greater than the thirdpulse duration 103, and the fourth deadtime duration 204 is less thanthe third deadtime duration 203.

The frequency detector then obtains a second resonant frequency valuebased on a sum of the third pulse duration 103, the third deadtimeduration 203, the fourth pulse duration 104, and the fourth deadtimeduration 204, in the same manner as the first resonant frequency valuewas obtained. The detected resonant frequency values become moreaccurate over time, so the second resonant frequency value obtained istypically closer to the actual resonant frequency of the corona igniter22 than the first resonant frequency value.

As shown in FIGS. 4 and 5, the method typically continues in the samemanner, preferably until the actual resonant frequency of the coronaigniter 22 is detected, or very close to being detected. A plurality ofadditional pulses of energy can be provided to the corona igniter 22after the fifth pulse of energy, wherein each additional pulse of energyis spaced from the next pulse by a deadtime duration during which noenergy is provided to the corona igniter 22. The pulse durationscontinuously increase over time and the deadtime durations continuouslydecrease over time.

The zero crossings and pulse durations are detected and evaluated toobtain additional resonant frequency values, in the same manner as thefirst and second resonant frequency values were obtained. Obtaining theadditional resonant frequency values is also conducted concurrently withoperation of the corona igniter 22, while energy is provided to thecorona igniter 22. The controller 28 can also continue to adjust thedrive frequency to match the obtained resonant frequency valuesconcurrent with operation of the corona igniter 22 to continuouslyimprove the performance of the system 20. Alternatively, the lastresonant frequency value obtained at the end of the resonant frequencydetection process, specifically the value based on the last two pulsedurations and last two deadtime durations, can be used as the startingdrive frequency in a future corona event, or as the drive frequencyduring a future corona event.

In addition to accurately detect the resonant frequency of the coronaigniter 22, the system is also able to make immediate adjustments to thedrive frequency, for example in response to resonant frequency changes,in order to maintain the drive frequency equal to, or very close to, theactual resonant frequency of the corona igniter 22. The system 20 isalso able to efficiently track and respond to resonant frequency changescaused by arcing events. Quick acquisition of the resonant frequency andrapid real-time adjustment of the drive frequency is possible tomaintain the best possible performance. It is also noted that othermethods of resonant frequency control which can be employed in thesystem described herein are disclosed in related U.S. patent applicationSer. Nos. 14/568,219, 14/568,330 and 14/568,438, which are incorporatedherein by reference. Each application lists the same inventor and wasfiled on the same day as the present application.

FIG. 1 is a block diagram of the corona discharge ignition system 20according to a first exemplary embodiment which is capable ofimplementing the concurrent method for resonant frequency detection ofthe present invention, and capable of rapidly responding to resonantfrequency changes and arc formation concurrent with operation of thecorona igniter 22, in order to maintain the drive frequency equal to orapproximately equal to the resonant frequency. In addition to thecontroller 28, switches 30A, 30B, corona igniter 22, induction coil L,and the current sensor 36 described above, the system 20 also includes apair of drivers 32A, 32B, referred to as a first driver 32A and a seconddriver 32B. The system 20 of FIG. 1 further includes a transformer 34, afirst low-pass filter 38, and a first signal conditioner 40. The voltageprovided to the corona igniter 22 and current flowing in the coronaigniter 22 is detected at the output 24.

The system 20 is controlled by the controller 28, which is preferably aprogrammable digital or mixed-signal controller, such as a digitalsignal processor (DSP), complex programmable logic device (CPLD),field-programmable gate array (FPGA), microcontroller, ormicroprocessor. The controller 28 receives a trigger input signal 42which commands the controller 28 to initiate the production of coronadischarge 26 in the combustion chamber. The controller 28 also providesan arc detect output signal 44 to inform any external control system(not shown) that an arc has been detected, and a feedback output signal46 to provide additional data about the health and operation of thecircuit to any external control system. The trigger input signal 42, arcdetect output signal 44, and feedback output signal 46 conveyed to andfrom the controller 28 are filtered by electromagnetic capabilityfilters, referred to as EMC filters 48, and other input filters 49. Inresponse to the trigger input signal 42, the controller 28 provides thedrive signals 50 to the drivers 32A, 32B which control the switches 30A,30B. When one of the switches 30A or 30B is active, the energy supplyV3, which is a DC voltage, is applied to a primary winding 52 of thetransformer 34. The transformer 34 then provides energy through theoutput 24 and to the corona igniter 22 at the drive frequency. In theexemplary embodiment, the transformer 34 has a configuration known inthe art as a “push-pull” configuration.

In the system 20 of FIG. 1, the current flowing in the corona igniter 22(the output current) is measured at the output 24 by the first currentsensor 36. The first current sensor 36 can also collect informationabout the voltage provided to the corona igniter 22 at the output 24,such as the length of the pulse durations 101, 102, 103, 104 and thedeadtime durations 201, 202, 203, 204. The first current sensor 36 canbe a shunt resistor, hall-effect sensor, or current transformer, forexample. The current sensor 36 identifies the zero crossing of thecurrent during each deadtime duration 201, 202, 203, 204, and sends theoutput signal 54 including this information toward the controller 28.The first current sensor 36 can use various different techniques toidentify the zero crossing. The current sensor can also determine thelength of the pulse durations 101, 102, 103, 104 and the length of thedeadtime durations 201, 202, 203, 204, and can send this information inthe output signal 54.

Preferably, the output signal 54 is lightly filtered by the firstlow-pass filter 38 before being conveyed to the controller 28. The firstlow-pass filter 38 creates a phase shift in the output signal 54 whichis smaller than the period of oscillation of the current. In oneembodiment, the phase shift is 180 degrees, but preferably the phaseshift is less than 180 degrees, and more preferably the phase shift isless than 90 degrees, which is less than one half cycle. The firstlow-pass filter 38 also removes unwanted high frequency noise generatedby switching high current and voltages. The filtered output signal 54 isthen transferred to the first signal conditioner 40, which makes theoutput signal 54 safe for transferring to the controller 28. Thus, theoutput signal 54 is at a level that can be safely handled by thecontroller 28. The output signal 54 is typically provided to thecontroller 28 after each zero crossing.

The controller 28 receives the output signal 54 with the current andvoltage information obtained by the first current sensor 36, and usesthe information to initiate correct timing of the switches 30A, 30B. Thelength of the first pulse duration 101 is predetermined by thecontroller 28 before the corona event, but the first deadtime duration201 is not predetermined. Thus, the controller 28 monitors the currentflowing in the corona igniter 22 for the zero crossing via the outputsignal 54. The zero crossing detection is preferably corrected toaccount for any delay in measuring the current, delay in the firstlow-pass filter 38, and the delay in other analogue or digital circuitelements. Immediately upon identifying the zero crossing of the current,the controller 28 terminates the first deadtime duration 201 byactivating one of the switches 30A, 30B.

The controller 28 also uses the information contained in the outputsignal 54 to identify the resonant frequency of the corona igniter 22concurrent with operation of the corona igniter 22. As discussed above,the controller 28 can use various different techniques to identify theresonant frequency value based on the sum of the pulse durations 101,102, 103, 104 and the deadtime durations 201, 202, 203, 204. Once theresonant frequency value is obtained, the controller 28 activates theswitches 30A, 30B at the correct times so that the drive frequency isequal to that resonant frequency value.

In the exemplary embodiment, once the controller 28 determines thetiming of the first switch 30A or second switch 30B required, thecontroller 28 instructs the first driver 32A to activate the firstswitch 30A or instructs the second driver 32B to activate the secondswitch 30B at the required time. The drivers 32A, 32B are instructed toactivate the switches 30A, 30B at the predetermined times, so that thedrive frequency of the energy conveyed through the switches 30A, 30B tothe transformer 34 and ultimately to the corona igniter 22 is equal tothe resonant frequency value of the corona igniter 22 obtained by thecontroller 28. The controller 28 can also adjust the timing of theswitches 30A, 30B whenever needed, for example in response to changes ofconditions in the system 20, concurrent with operation of the coronaigniter 22.

FIG. 2 is a block diagram of a corona discharge 26 ignition system 20according to a second exemplary embodiment of the invention, whichoperates like the system 20 of FIG. 1, but includes several additionalfeatures. One additional feature is that that the various functionalsections of the system 20 include a control system ground 56, a powersystem ground 58, and load ground 60 which are separated from oneanother. This technique is used to improve EMI and/or electromagneticcapability (EMC). The control system ground 56 is isolated from a powersystem ground 58 by galvanic isolation 62. The transformer 34 isolatesthe power system ground 58 from the load ground 60, and this isolationmust be maintained between the first current sensor 36 and thecontroller 28. The isolation between the power system ground 58 and theload ground 60 may be achieved by adding galvanic isolation 62 at thefirst low-pass filter 38 or the first signal conditioner 40.Alternatively, the isolation between the power system ground 58 and theload ground 60 can be achieved by operating the first low-pass filter 38or the first signal conditioner 40 in a differential mode where only anegligible current can flow through the device. In the system 20 of FIG.2, only the first signal conditioner 40 operates in differential mode toisolate the power system ground 58 from the load ground 60. One or moreof these methods may be employed.

Another additional feature of the system 20 of FIG. 2 is a secondcurrent sensor 64 to measure the amplitude of the current in the secondswitch 30B on the primary side of the transformer 34. The second currentsensor 64 specifically measures the current at the output of the secondswitch 30B. Alternatively, there could be a second current sensor 64 ateach of the switches 30A, 30B. The second current sensor 64 provides anadditional feedback signal 55 to the controller 28, giving valuablediagnostic information which is not possible through the phasemeasurement of only the first current sensor 36. For example, it ispossible to detect an open or short circuit in the load circuit bymeasuring the current at the output of the switches 30A, 30B. Inaddition, the system 20 of FIG. 2 includes a second low-pass filter 66located between the current sensor and the controller 28 to lightlyfilter the current output signal 54 before providing the feedback signal55 to the controller 28.

FIG. 3 is a block diagram of a corona discharge 26 ignition system 20according to a third exemplary embodiment of the invention. The system20 of FIG. 3 also includes the galvanic isolation 62, but in thisembodiment, the galvanic isolation 62 is located on both the energyinput and energy output sides of the controller 28, and completelyseparates the three grounds 56, 58, 60. One or both of the barriersprovided by the galvanic isolation 62 can be omitted if the circuit isdesigned to operate using fewer grounds.

The system 20 of FIG. 3 further includes another winding, referred to asa voltage feedback winding 68. The voltage provided by the voltagefeedback winding 68 reflects the voltage at the output 24 of the coronaigniter 22. A voltage sensor 78 is preferably located at the output ofthe voltage feedback winding 68 to measure this voltage. An outputsignal 80 including the output voltage is then transferred through thesecond low-pass filter 66 to the controller 28. The second low-passfilter 66 lightly filters the voltage output signal 80 before providingthe output signal 80 to the controller 28. The controller 28 candetermine the length of the pulse durations 101, 102, 103, 104 and thelength of the deadtime durations 201, 202, 203, 204 from the informationcontained in this output signal 80. Also, unlike the systems 20 of FIGS.1 and 2, a control signal 72 is provided to the controller 28 of FIG. 3.The control signal 72 can include any information related to operationof the corona igniter 22, such as whether arcing occurred or the desiredvoltage.

The features of the exemplary systems 20 shown in FIGS. 1-3, as well asthose shown in the related applications, may be used in variouscombinations, other than those specifically described herein. However,the system 20 should have the ability to drive the corona igniter 22with an AC signal at or near its resonant frequency; enable and disablethis AC drive signal; adjust the duty cycle of the voltage supplied tothe corona igniter 22 independent of the frequency of the voltagesupplied to the corona igniter 22.

The system 20 and method of the present invention provides multipleadvantages over comparative systems. As discussed above, the system andmethod can detect a resonant frequency value that is equal to, or veryclose to, the actual resonant frequency of the corona igniter 22concurrent with operation of the corona igniter 22. A completemeasurement of the resonant frequency after each cycle can be made, andthe measurement can be evaluated and used on a per-cycle basis.Measurement over multiple cycles can also be done to improve theaccuracy of the resonant frequency value detected. Immediate adjustmentsof the drive frequency can be made to maintain the drive frequency at orclose to the actual resonant frequency of the corona igniter 22 and thusmaintain a robust corona discharge 26.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings and may be practicedotherwise than as specifically described while within the scope of theclaims.

What is claimed is:
 1. A system for detecting the resonant frequency ofa corona igniter in a corona ignition system, comprising: a first switchproviding a first pulse of energy from an energy supply to a coronaigniter at a positive voltage for a first pulse duration causing currentto flow in the corona igniter; the first switch ceasing the first pulseduration before the current in the corona igniter crosses through zeroand providing no energy to the corona igniter for a first deadtimeduration immediately upon ceasing the first pulse duration; a frequencydetector detecting when the current flowing in the corona ignitercrosses through zero during the first deadtime duration and initiating adrive signal to provide a second pulse of energy to the corona igniterin response to the zero crossing of the current; a second switchreceiving the drive signal and providing the second pulse of energy fromthe energy supply to the corona igniter at a negative voltage for asecond pulse duration to cease the first deadtime duration; the secondswitch ceasing the second pulse duration before the current flowing inthe corona igniter crosses through zero and providing no energy to thecorona igniter for a second deadtime duration immediately upon ceasingthe second pulse duration; the frequency detector detecting when thecurrent flowing in the corona igniter crosses through zero during thesecond deadtime duration and initiating a drive signal to provide athird pulse of energy to the corona igniter in response to the zerocrossing of the current; the first switch receiving the drive signal andproviding the third pulse of energy from the energy supply to the coronaigniter at a positive voltage to cease the second deadtime duration; andthe frequency detector obtaining a first resonant frequency value basedon a sum of the first pulse duration, the first deadtime duration, thesecond pulse duration, and the second deadtime duration.
 2. The systemof claim 1, wherein the frequency detector includes a current sensorobtaining the current flowing in the corona igniter and determining thezero crossings of the current.
 3. The system of claim 2, wherein thefrequency detector includes a controller for receiving the detected zerocrossings of the current from the current sensor; and determining thefirst resonant frequency value based on a sum of the first pulseduration, the first deadtime duration, the second pulse duration, andthe second deadtime duration.
 4. The system of claim 3, wherein thecontroller adjusts a drive frequency of the energy provided to thecorona igniter to match the obtained first resonant frequency valuewhile energy is provided to the corona igniter.
 5. The system of claim3, wherein the controller sets the first pulse duration based on anydelays of components of the system so that the first pulse durationceases before the current flowing in the corona igniter crosses throughzero.
 6. The system of claim 1, wherein the first switch provides thethird pulse of energy from the energy supply to the corona igniter for athird pulse duration; the first switch ceases the third pulse durationbefore the current flowing in the corona igniter crosses through zeroand provides no energy to the corona igniter for a third deadtimeduration immediately upon ceasing the third pulse duration; thefrequency detector detects when the current flowing in the coronaigniter crosses through zero during the third deadtime duration andinitiates a drive signal to provide a fourth pulse of energy to thecorona igniter in response to the zero crossing of the current; thesecond switch receives the drive signal and provides the fourth pulse ofenergy from the energy supply to the corona igniter at a negativevoltage for a fourth pulse duration to cease the third deadtimeduration; the second switch ceases the fourth pulse duration before thecurrent flowing in the corona igniter crosses through zero and providesno energy to the corona igniter for a fourth deadtime durationimmediately upon ceasing the fourth pulse duration; the frequencydetector detects when the current flowing in the corona igniter crossesthrough zero during the fourth deadtime duration and initiates a drivesignal to provide a fifth pulse of energy to the corona igniter inresponse to the zero crossing of the current; the first switch providesa fifth pulse of energy to the corona igniter at a positive voltage inresponse to the zero crossing of the current to cease the fourthdeadtime duration; and the frequency detector obtains a second resonantfrequency value based on a sum of the third pulse duration, the thirddeadtime duration, the fourth pulse duration, and the fourth deadtimeduration.
 7. The system of claim 6, wherein the steps of obtaining thefirst resonant frequency value and the second resonant frequency valueare conducted while energy is provided to the corona igniter and whilethe corona igniter provides a corona discharge.
 8. The system of claim6, wherein the fourth pulse duration is greater than the third pulseduration and the fourth deadtime duration is less than the thirddeadtime duration.
 9. The method of claim 6, wherein the switchesprovide a plurality of pulses of energy from the energy supply to thecorona igniter after the fifth pulse of energy, each of the pulses ofenergy are provided for a pulse duration and are spaced from one anotherby a deadtime duration during which no energy is provided to the coronaigniter, the pulse durations increase over time, and the deadtimedurations decrease over time.
 10. A system for detecting the resonantfrequency of a corona igniter in a corona ignition system, comprising: afirst switch providing a first pulse of energy from an energy supply toa corona igniter at a positive voltage for a first pulse durationcausing current to flow in the corona igniter; the first switch ceasingthe first pulse duration before the current in the corona ignitercrosses through zero and providing no energy to the corona igniter for afirst deadtime duration immediately upon ceasing the first pulse ofenergy; a frequency detector detecting when the current flowing in thecorona igniter crosses through zero during the first deadtime durationand initiating a drive signal to provide a second pulse of energy to thecorona igniter in response to the first zero crossing of the current;the frequency detector obtaining a first zero crossing duration, whereinthe first zero crossing duration begins at the start of the first pulseof energy and ends at the first zero crossing; a second switch receivingthe drive signal and providing the second pulse of energy from theenergy supply to the corona igniter at a negative voltage for a secondpulse duration to cease the first deadtime duration; the second switchceasing the second pulse duration before the current flowing in thecorona igniter crosses through zero and providing no energy to thecorona igniter for a second deadtime duration immediately upon ceasingthe second pulse of energy; the frequency detector detecting when thecurrent flowing in the corona igniter crosses through zero during thesecond deadtime duration; the frequency detector obtaining a second zerocrossing duration, wherein the second zero crossing duration begins atthe first zero crossing and ends at the second zero crossing; and thefrequency detector obtaining a first resonant frequency value based on asum of the first zero crossing duration and the second zero crossingduration.
 11. The system of claim 10, wherein the frequency detectorincludes a current sensor obtaining the current flowing in the coronaigniter and determining the zero crossings of the current.
 12. Thesystem of claim 10, wherein the step of obtaining the first resonantfrequency value is conducted while energy is provided to the coronaigniter and while the corona igniter provides a corona discharge. 13.The system of claim 11, wherein the frequency detector includes acontroller for receiving the detected zero crossings of the current fromthe current sensor.
 14. The system of claim 13, wherein the controllerdetermines the first resonant frequency value based on a sum of thefirst pulse duration, the first deadtime duration, the second pulseduration, and the second deadtime duration.
 15. The system of claim 13,wherein the controller adjusts a drive frequency of the energy providedto the corona igniter to match the obtained first resonant frequencyvalue while energy is provided to the corona igniter.
 16. The system ofclaim 13, wherein the controller sets the first pulse duration based onany delays of components of the system so that the first pulse durationceases before the current flowing in the corona igniter crosses throughzero.